1. Field of the Invention
The present invention relates to an artificially synthesized gene encoding an active protein. More specifically, the present invention relates to an artificially synthesized gene encoding a protein having a trypsin inhibitor activity. The present invention also relates to a plant which expresses a gene encoding a protein having trypsin inhibitor activity, which also confers resistance to lepidopteran insect pests.
2. Description of the Related Art
There exist several protease inhibitors including trypsin inhibitors in Fabaceae plant (Yamamoto et al. J. Biochem. 94, pp. 849-863, 1983).
The trypsin inhibitors derived from Fabaceae plant are classified into two groups on the basis of their molecular weight and cystine content. One is the Bowman-Birk type inhibitors which have molecular weights of around 8,000 and are characterized by a high cystine content, namely seven disulfide bridges (Norioka et al., J. Biochem. 94, pp. 589-599). The other is the Kunitz type inhibitors which have molecular weights of around 20,000 and include two disulfide bridges (Shibata et al., J. Biochem. 99: pp. 1147-1155, 1986). The Kunitz type inhibitors are known to exist not only in Fabaceae plant but also in soybean, silk tree, barley, acacia, and rice (Yamamoto et al. J. Biochem. 94, pp. 849-863, 1983). Trypsin inhibitors are present in the pancreas and plasma of vertebrates as peptides which can inhibit the activity of the digestive enzyme, trypsin. Although the role of the trypsin inhibitor in a plant is not known very well, it has been reported that a trypsin inhibitor ingested by an insect inhabits growth of the insect (R. Johnson et al., Proc. Natl. Acad. Sci. USA 86, pp. 9871-9875, 1989).
A trypsin inhibitor WTI-1b derived from the winged bean (Psophocarpus tetragonolobus (L.) DC.) is a Knitz type inhibitor which has molecular weight of 19,200, and the complete amino acid sequence of the purified protein has been identified (Yamamoto et al. J. Biochem. 94, pp. 849-863, 1983). A gene encoding the WTI-1b has not been isolated.